i have to agree with most. The tank is way to small for the stock list you have. If it was me i would either upgade to a much bigger tank and if thats not an option, i would keep one and rehome the rest. though i think adventually your going to need a bigger tank for just houseing one of them. a 55 might be to small to house any one of them for life.
x2..lol.. I've had similiar mixes in a grow out tank before. Some fish are psychos -- others grow up to be psychos -- and some have no issues with tankmates at all... You really never can tell.
That is the reason why I went with plecos and characins. I have had parachromis cichlids and other bruisers before and it always ends up the same. 1 fish per tank. I had an adult Vieja Argentae at 12 inches that took over a 300 gallon tank. I couldn't keep anything with that fish. Thanks to my nephew and tonka trucks that tank was cracked. I traded the bruiser in for a 4 foot tank and now keep an adult L-114 pleco and a school of silver dollars in harmony. MY piont never had luck keeping the "take no prisoners cichlids" other thab alone. Although others on here can make it work.